Dental laboratory components and procedures for anatomical restoration on artificial root fixtures

ABSTRACT

A second-stage healing abutment for forming and preserving in the mucosa above a dental implant a transmucosal opening large enough to receive an artificial tooth which faithfully replicates a natural tooth being restored, and a companion transfer coping having identical transmucosal portions for forming in a laboratory model a faithful replica of the transmucosal opening in which to fabricate the artificial tooth, and methods of using the same.

BACKGROUND OF THE INVENTION

The field of restorative dentistry using artificial roots in the presently-preferred form of osseointegrated cylinder-shaped dental implant fixtures has progressed to the level where attention is now being given to providing restorations on them that closely replicate natural dentition in appearance, especially where the teeth emerge from the gums. The problems of achieving a natural-looking emergence profile are addressed using a technique for fabricating implant-supported restorations directly to an implant fixture, employing custom wax patterns fashioned on abutment cylinders to achieve, for example, a custom-made porcelain-fused-to-metal restoration. This technique is described in published articles which appeared in The International Journal of Oral & Maxillofacial Implants, Vol. 3, Number 1, 1988 at pages 25-26 "Single-Tooth Implant Supported Restorations" Lewis, S. G. et al., and Number 3, 1988 at pages 183-189 "The "UCLA" Abutment", Lewis, S. et al. A similar result using a different abutment is described in U.S. Pat. No. 4,988,298, which is owned by the Assignee of the present invention. The problem is incompletely addressed in U.S. Pat. No. 5,073,111 issued to Daftary Dec. 17, 1991.

The dental restoration of a wholly or partially edentulous patient with dentition supported on dental implant fixtures is now frequently done in two stages. In the first stage the implant fixture is placed and left to integrate with the jawbone. The second stage begins with re-accessing the fixture through the gum and maintaining access with a healing cap or the like, and continues through the fabrication of restorative dentition in the laboratory using measurements and other information taken from time to time from the patient. During that time the patient may have only a healing cap in his or her mouth, or according to more recent and sophisticated procedures the patient may be fitted with temporary dentition from which additional refining measurements can be taken. However, the healing abutments and the transfer copings or pick-up copings of the prior art do not cooperate to provide room for making and installing on the implant an artificial tooth having an aesthetically-pleasing or anatomically-correct emergence profile. The gingival aspect of an implant fixture is, typically not more than about 4.1 mm in diameter, whereas the longer (mesial-distal) dimension of a natural tooth where it emerges from the gum is between about 4.5 mm and about 8.0 mm. According to present practice, healing abutments, which are cylindrical in cross-section, are chosen to approximate the mesial-distal dimension of the tooth being replaced. At the same time, the transfer or pick-up copings of the prior art are all one size, about 4.5 mm in diameter. As a result, a gap is left in the gingiva, around the coping, and impression material fills this gap when an impression is taken. The gingiva also tend to collapse into this gap, resulting in less than accurate replication of the conditions in the patient's mouth. As a further consequence of these problems it is difficult to make soft tissue models accurately. Stone models replicate these errors, and this requires technicians to shape the stone manually to comply with the conditions in the patient's mouth, or risk producing a crown with an inaccurate emergence profile or crown-to-abutment margin which are misplaced. These are severe problems, resulting from the fact that the designers of prior art components have thus far failed to recognize them. The present invention teaches new surgical and laboratory components, and new procedures, which eliminate such inaccurate and time-wasting procedures, and improve the art of making anatomically-correct and aesthetically-pleasing dental restorations.

GENERAL NATURE OF THE INVENTION

In accordance with the present invention a healing cap or healing abutment sized to maintain space for a desired emergence profile through the gum is used at the beginning of the second stage, in combination with an impression coping or a pick-up coping having similar size specifications so that when the impression coping is fitted to the implant fixture for taking the impression from which the stone model will be made the space for the desired emergence profile established in the gum by the healing abutment or cap will be preserved and replicated in the stone model and in a soft-tissue model, if desired. From such models restorative dentition can be fabricated without requiring the use of a specially contoured tooth-support abutment as taught by Daftary, for example. Rather, artificial teeth replicating in all material respects the natural teeth that they replace can be fashioned on the model using components that have become standard in the art.

In one of its aspects the invention teaches a new method of preparing an aesthetically pleasing, as well as anatomically correct dental restoration on a natural or artificial root comprising first the step of preparing in the gingiva overlying the root an opening to the gingival aspect of the root which opening is sufficient to accommodate the shape and contour of a natural tooth emerging through the gingiva from the root, followed by the step of making a rigid (e.g.: stone) model that reproduces in stone or in overlying soft-tissue exactly that opening and gingival aspect of the root, and then the step of forming on the model an artificial tooth which replicates in that opening the shape, size and contour desired in the restoration, and finally installing that restoration on the root. In another aspect the invention provides a healing member (sometimes called a cap, abutment or screw) which has a transmucosal section having at one end the subgingival cross-sectional size and shape of the artificial root and where it emerges from the gingivae the mesial-distal size of the natural tooth being replaced, and means to attach that healing member non-rotatively to the root, for establishing the above-mentioned opening in the gingiva. In another aspect the invention provides a transfer coping for use in making the above-mentioned rigid model having a transmucosal section that is substantially identical in cross-sectioned size and shape to the transmucosal section of the healing member so as to fit fully within the opening in the gingiva that was formed by the healing member, and a supragingival section shaped for non-rotational embedment in resilient modelling material, together with means to attach the coping non-rotatively to the root. In still another aspect the invention provides sets of matched pairs of healing members and transfer copings shaped and sized for use according to the invention to prepare restorations of particular types of teeth, such as molars, premolars, bicuspids and incisors, as examples.

These and other features of the invention will be explained in greater detail in the following description of certain exemplary embodiments of the invention referring to the accompanying drawings in which:

FIG. 1 is a longitudinal section which shows an implant fixture installed in bone with a healing cap in place;

FIG. 2 shows a natural bicuspid;

FIG. 3 is a longitudinal section which shows a transfer coping used to make an impression;

FIG. 4 is a longitudinal section which shows a stone model made from the impression;

FIG. 5 shows the invention as used to replicate the natural tooth of FIG. 2;

FIG. 6 shows the cross-section of a natural emergence profile which the invention can replicate;

FIG. 7 is a cross-section which shows a soft-tissue model; and

FIG. 8 shows a pick-up coping used to make an impression.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a dental implant fixture 10 osseointegrated type installed in a section of jawbone 12. The "second stage surgery" has begun, and a healing abutment 14 is in place on the implant fixture. In order to provide for a more natural emergence profile in the final restoration, this abutment expands in a tapered transmucosal section 15 from the end contacting the implant fixture toward the outer surface 16 of the surrounding gingiva 18, beyond which the walls 17 of the abutment extend vertically. As shown in FIG. 1, a portion of the vertical walls 17 is immersed in the gum tissue, below the outer surface 16, together with the tapered section 15. The implant fixture has an internally threaded bore 20 axially located in it, surrounded at its gingival opening by a non-round boss 22, the external cross-section of which typically is hexagonal. The healing abutment 14 has a corresponding non-round socket 24 enveloping the boss 22. In the illustrated embodiment through-bolt 26 passing through an axial bore 28 in the healing abutment is used to attach the abutment to the implant fixture, in a well known manner. Attached in this manner, the healing abutment is not able to be rotated around the axis of the bolt. Having regard to the fact that few if any natural teeth are round in cross-section where they emerge from the gums, this feature of the invention makes it possible to prepare dental restorations with emergence profiles that are not round. To this end healing abutments according to the invention may be prefabricated with a transmucosal section 15 having at the gingival surface 16 a round cross-sectional shape the diameter of which is approximately equal to the mesial-distal dimension of the lost tooth being restored. Alternatively, the peripheral contour in the tapered section 15 may closely replicate the emergence profile of the natural tooth which was in the site where the implant fixture 10 is installed. The invention contemplates providing sets of such prefabricated healing abutments, together with matching impression copings. The supragingival vertical walls of the healing abutment and the impression copings used with it may also be contoured to mimic the natural tooth cross-section, depending on the thickness of the gingiva 18 and the corresponding vertical dimension of the abutment.

FIG. 2 shows the general contours of a bicuspid 30 emerging from the outer surface 16 of the gingiva. A typical bicuspid is approximately 5.5 mm in mesial-distal dimension at the surface 16.

A typical standard abutment or impression coping is at most 4.5 mm in diameter. Some teeth, e.g.: molars, may be as much as 6.0 or 7.0 mm in mesial-distal dimension. Moreover, as appears in FIG. 6, which illustrates the cross-section of an emergence profile 75 characteristic of an anterior tooth (not shown), it is also desirable to be able to provide for emergence profiles the cross-sections of which do not even approximate round. To address these problems the invention provides methods and means to create and preserve openings in the gingiva 18 which are significantly larger than the cross-section of the implant fixture 10 and which may be round, or may have any desirable shape, and to preserve each such opening throughout the laboratory procedure for making and fitting the relevant dental restoration. Thus, as has been mentioned, the cross-sectional shape of the transmucosal tapered portion 15 and the vertical wall portion 17 of the healing abutment can be round as long as its diameter approximates the mesial-distal size of the natural tooth. These parts need not be round, but rather they may be sized and shaped to match the cross-sectional shape of the emergence profile of the missing tooth that is intended to be replicated and installed on the implant fixture 10.

FIG. 3 shows a transfer coping 35 of a kind used to take impressions, buried in an impression material 36. The essential structure of this impression coping is described and claimed in U.S. Pat. No. 4,955,811, which is owned by the Assignee of the present invention. This impression coping has a flat surface 37 for locating it non-rotationally in the impression material, a hexagonal socket 38 in its base 39 for fixing it non-rotationally on the implant fixture 10, an axial thought-bore 40 and a bolt 41 with an expanded head 42 for holding it in the impression material. The bolt 41 is used to attach the impression coping 35 to the implant fixture 10. For the purposes of the present invention the impression coping has a tapered section 44 at its end surrounding the socket 38 which replicates in size and shape the tapered transmucosal section 15 of the healing abutment 14. As shown in FIG. 3, a portion of the base 39 emerges from the impression material 36, together with the tapered section 44. The base 39 may also be contoured to mimic the natural cross-section of the tooth being replaced, as is mentioned above.

FIG. 4 is a stone model 50 of the patient's implant installation site shown in FIG. 1. An implant replica 54 is encased in stone 52, according to well-known dental laboratory practice. The replica 54 has a threaded bore 20' and non-round boss 22' which are identical to the bore 20 and boss 22 of the implant fixture 10. A tapered recess 56 in the surface of the stone surrounding the end of the replica 54 matches in size and shape the tapered section 44 and a part of the base 39 of the impression coping 35. Thus the healing abutment fits equally well on the implant replica as on the implant fixture.

The illustration in FIGS. 1, 3 and 4 of a process in which the openings in the gingiva 18 and the model 50 have a "vertical" portion as well as the tapered portion is exemplary only, and is not intended to limit the invention to that feature.

An artificial bicuspid 60 as shown in FIG. 5 can be made with the aid of the model 50. A known form of core 62 is non-rotatively attachable to the implant replica with a screw bolt 64, passed through a through-bore 66 in the core. The head 68 of the bolt comes to rest on a shoulder 70 in the core 62, holding the core firmly attached to the implant replica 54 within the tapered recess 56. The artificial tooth is fashioned on the core using any available dental material, such as porcelain or acrylic, for example. The dental material extends well within the tapered recess 56, so that outside this recess the core material cannot be seen. The core itself can be made of any suitable rigid material, such as titanium and its dilute alloys. After being fashioned and anatomically shaped as desired the artificial tooth 60 can be transferred to the implant fixture 10 and its appearance will be as is shown in FIG. 2. It will emerge from the gingiva 18 looking exactly the same as a natural tooth. According to well-known dental practice, the opening into the core at the top of the tooth 60 will be filled with a suitable dental cement or the like and polished so as to be for all practical purposes not distinguishable from the rest of the tooth. The above-mentioned U.S. Pat. No. 4,988,298 illustrates an artificial tooth that can benefit from the invention.

Because the component parts used in this invention can be made so that they are non-rotatably attachable together, it is not necessary that they be cylindrical in cross-section where they are attachable one to the other. Thus the healing abutment 14, the base 39 of the impression coping 35, and the subgingival section of the artificial tooth 60 can each be given the same cross-sectional size and shape, changing gradually from round at the subgingival aspect of the implant fixture 10 to non-round proceeding toward the gingival surface through which the artificial tooth will emerge from the surface 16 of the overlying gingiva. In this manner that size and shape can initially be established by the healing abutment in the opening through the gingiva 18, and the same size and shape in the correct orientation around the axis of the implant fixture 10 can be replicated and preserved in the model 50, thereby enabling the tooth 60 to be formed in the laboratory with the correct emergence profile. This feature of the invention is particularly advantageous when restoring anterior dentition, where the emergence cross-section, e.g.: 75 as is indicated in FIG. 6, has segments that are almost straight, and curved segments that turn on short radii.

The invention is not limited to the use of non-rotatively attachable components. In its more general aspects, the invention contemplates providing transmucosal openings which may be round with a diameter which approximates the mesial-distal dimension of the missing tooth that is being replaced, and preserving that dimension in a round opening throughout the laboratory procedure. This simple arrangement provides the basic advantages of the invention, which include eliminating the need to surgically expand a trans-tissue opening that was originally or has become too small to receive the restoration, and eliminating the need for laboratory technicians to hand-finish stone models in which the trans-tissue opening was incorrectly formed due to causes that are mentioned above. Provided the trans-tissue opening is formed and maintained large enough to receive the restoration, last-minute surgery is not needed, and the tissue will grow to the restoration. Referring to FIG. 6, the dashed-line circle 74 represents a trans-tissue opening that is larger than the tooth 75. In this situation, there is no need to provide the non-rotative features such as the mating non-round boss 22 and socket 24.

According to the invention healing abutments 14 and transfer copings 35 may be prefabricated in sets of pairs, each pair having an "emergence profile contour" that is representative of a range of teeth of a particular type; that is, for example, large molars, small molars, pre-molars, bicuspids and anterior incisors. The restorative dentist may then choose a pair which most closely replicates the emergence profile that is desired, modify the members of that pair if such is deemed necessary or desirable, and then make a restoration in accordance with the present invention that will be aesthetically pleasing and very close to anatomically correct.

FIG. 7 shows a stone model 50' similar to the model 50 of FIG. 4, but in cross-section rather than in longitudinal section, and including a stone foundation 52' rigidly holding an implant replica 54'. A soft-tissue layer 80, which replicates the human gingiva 18, overlies the stone part. This layer can be made of any suitable plastics or rubber-like material having physical properties such as softness and elasticity that resemble the physical properties of human gum tissue. Certain silicone-based rubber and plastics materials are suitable, preference being given to those which can be fabricated from a soft flowable state. In use, the soft flowable plastics material is placed in the impression around the tapered section 44 and emerging portion of the base 39 of the transfer coping 35 to a thickness the same as that of the patient's gingiva 18. The resulting opening 82 is similar to the opening 56 in the stone that is shown in FIG. 4. It has the advantage that the laboratory technician can manipulate the model exactly as the dentist manipulates the patient's gingiva.

FIG. 8 shows a pick-up impression coping 85 buried in an impression material 36'. This impression coping has a non-round head portion 87 for anchoring the coping non-rotationally in the impression material, a hexagonal socket 38' in its base 89 for fixing it non-rotationally on the implant fixture if desired, an axial through bore 40' and a bolt 41' passing through this bore to attach the impression coping to the implant fixture. The proximal end 42' of the bolt has no expanded head on it for the reason that in use when an impression is taken this end of the bolt extends through a hole in the impression tray (not shown) and, when the impression material has set up in the tray the bolt 41' is unscrewed from the implant fixture by accessing its proximal end 42' from outside the tray and the coping 85 remains in (is "picked-up" by) the impression material, being anchored therein by its expanded head 87. For the purposes of this invention the pick-up coping 85 functions like the transfer coping 35 of FIG. 3. Thus, the base 89 is expanded to a diameter which approximates the mesial-distal dimension of the natural tooth that is being restored and the tapered section 84 reduces subgingivally to the diameter of the implant fixture or other underlying support that may be present. Like the base 39 in FIG. 3, the base 89 may be contoured to mimic the cross-section of the natural tooth. 

We claim:
 1. A method of preparing an anatomically correct dental restoration for installation on a natural or artificial root comprising the steps of preparing in the gingiva overlying said root an opening to the gingival aspect of said root said opening having at the gingival surface substantially the full cross-sectional size and non-round shape of a natural tooth emerging through said gingiva from said root, making a model of said gingiva replicating substantially identically said opening and said gingival aspect of sad root, forming on said model an artificial tooth substantially replicating in said opening the emergence shape and contours of said natural tooth, and installing said artificial tooth on said root.
 2. A method according to claim 1 in which the cross-sectional dimension of said opening at said gingival aspect of said root is substantially similar to that of said root and said dimension changes gradually to a larger opening as it proceeds through said gingiva to said surface.
 3. A method according to claim 2 in which the cross-sectional shape of said opening at the surface of said gingiva is substantially similar to the non-round-cross-sectional shape of said natural tooth at said surface.
 4. A method according to claim 1 including file step of forming an initial opening in said gingiva, fixing to said root a component having a transmucosal part in said initial opening and a subgingival end confronting said root, the cross-section of said subgingival end being substantially similar in size and shape to the confronting cross-section of said root, the cross-section of said transmucosal part enlarging to substantially said full cross-sectional size and non-round shape where it emerges from said gingiva.
 5. A method according to claim 4 in which the shape of said cross-section of said transmucosal part at the surface of said gingiva is substantially similar to the non-round cross-sectional shape of said natural tooth at said surface.
 6. A method according to claim 4 in which said component is a healing member and said healing member is left in place on said root for a period of time in order to form said opening to said size and non-round shape.
 7. A method according to claim 6 including the further steps of removing said healing member from said root and substituting for it a transfer coping having a substantially similar transmucosal part, making a rotation-inhibiting impression of said coping and surrounding gingiva, and making said model from said impression with said coping in it.
 8. A healing member for use in dental implant surgery following placement of a dental implant fixture at an edentulous site in a patient's jawbone, said member having a transmucosal section for establishing through the mucosa overlying said jawbone at said site an opening exposing the sub-gingival end of said fixture, said section having at one end substantially the cross-sectional size and shape of said end of said fixture, said section having at its other end substantially the cross-sectional size and non-round shape of a natural tooth at said site where said tooth emerges from said mucosa, and means to attach said one end of said member to said fixture.
 9. A healing member according to claim 8 in which the cross-section of said transmucosal section is substantially round at said one end and changes gradually to non-round where it emerges from said mucosa.
 10. A transfer coping for use in making a rigid model of a patient's edentulous jawbone site containing root means in the jawbone and an opening through the overlying mucosa exposing the gingival end of said root means, which opening has at one end substantially the cross-sectional size and shape of said gingival end and at its other end substantially the cross-sectional size and non-round shape of a natural tooth at said site where said tooth emerges through the surface of said mucosa, said coping having a transmucosal section sized and having a non-round shape so as to substantially mate with the size and non-round shape of said opening and a supragingival section adapted for embedment in resilient modelling material, said supragingival section including means to restrain said coping against turning in said modelling material, and means to attach said transmucosal section to said root means within said opening.
 11. A coping according to claim 10 in which the cross-section of said transmucosal section is substantially round at its end confronting said root means and changes gradually to non-round as it proceeds towards said surface of said gingiva.
 12. A coping according to claim 11 in which the cross-sectional shape of said transmucosal section at said surface is substantially similar to the cross-sectional shape of said natural tooth at said surface.
 13. A set of components for use in making an artificial tooth which emulates a natural tooth missing from a patient's jawbone site containing root means in said jawbone, said set including a healing member having a first transmucosal section for establishing in the mucosa overlying said jawbone at said site an opening exposing the gingival end of said root means through said mucosa, said first transmucosal section being attachable at one end to said root means, and having at said one end substantially the cross-sectional size of said gingival end and at its other end substantially the cross-sectional size and non-round shape of said natural tooth where said tooth emerged through the surface of said mucosa, means to attach said one end of said first transmucosal section to said gingival end, said set further including a transfer coping for making a rigid model of said site faithfully replicating said opening, said coping being attachable at one end to said gingival end, and having at said one end a second transmucosal section which is substantially identical to said first transmucosal section and remote from said one end a supragingival section adapted for embedment in resilient modelling material, means to attach said second transmucosal section to said root means through said opening, said supragingival section including means to restrain said coping against turning in said modelling material.
 14. A set of components according to claim 13 in which the cross-section of each of said transmucosal sections is substantially round at its end confronting said root means and said cross-section gradually changes to non-round as it proceeds toward said surface of said mucosa.
 15. A set of components according to claim 14 in which the cross-sectional shape of each of said transmucosal section at said surface is substantially similar to the cross-sectional shape of said natural tooth at said surface.
 16. A set of components according to claim 13 including means to lock said healing member against turning on said root means, and means to lock said coping against turning on said root means.
 17. A transfer coping according to claim 13 comprising an elongated body having said transmucosal section at said first end and said supragingival section at a second end, and a through bore between said ends for passage of bolt means to attach said transmucosal section to said root means.
 18. A transfer coping according to claim 17 in which a cross-sectional dimension of said transmucosal section is substantially larger than any cross-sectional dimension of said supragingival section.
 19. A transfer coping according to claim 18 is which said transmucosal section and said supragingival section are separated by an intermediate waist section having transverse dimensions that are smaller than any of said cross-sectional dimensions. 